The present disclosure relates to an exhaust gas arrangement comprising an exhaust gas system for conveying an exhaust gas stream, wherein the exhaust gas system comprises a turbine and an exhaust gas treatment system, wherein the exhaust gas arrangement further comprises a working fluid circulation circuit connected to said exhaust gas system for recovery of energy from the exhaust gas stream, wherein the working fluid circulation circuit comprises a first heat exchanger which is arranged at a waste heat source for heat exchange between the waste heat source and a working fluid in the working fluid circulation circuit, and a second heat exchanger positioned in the exhaust gas system for heat exchange between the exhaust gas and the working fluid. An internal combustion engine system and a vehicle comprising such an exhaust gas arrangement are also disclosed.
From the prior art a plurality of exhaust gas arrangements are known. One of them is based on a Rankin cycle which may use waste heat of an internal combustion engine, e.g. an exhaust gas system, for heating a working fluid which in turn drives an expander engine for generating electric or mechanical energy. One known exhaust gas arrangement is disclosed in EP 2 098 696 A1.
The working fluid of an exhaust gas arrangement based on a Rankin cycle usually cycles through four stages. In a first stage the liquid working fluid is pumped from low to high pressure. In the subsequent stage, the high pressure liquid working fluid is heated, e.g. by an external heat source, and thereby converted into its gaseous phase. In the next stage, the gaseous phase working fluid expands in an expander engine, e.g. a displacement expander, such as a piston engine and/or a turbine. In its last stage, the working fluid is cooled down in a condensation device and converted back to its liquid phase.
Usually, in a vehicle, the expander engine may either be connected to a generator generating electric energy for driving an energy consumer, or to the drivetrain thereby acting as auxiliary power unit for the internal combustion engine in the vehicle.
The internal combustion engine (ICE) in turn may be operated in at least four main ICE operation modes. In the following, the term “ICE operation modes” is used as abbreviation of “internal combustion engine operation modes”:
i. “High load ICE operation modes” are defined as ICE operation modes where the driving situation requires a lot of driving force, e.g. running uphill or accelerating.
ii. “Normal load ICE operation modes” are defined as ICE operation modes where the vehicle is neither substantially accelerating nor substantially decelerating, e.g. the vehicle is running at constant speed on a high way.
iii. “Low load ICE operation modes” are defined as ICE operation modes, where the vehicle requires little driving force, e.g. when the vehicle is running downhill, decelerates or is in motoring or idle engine operation modes (see further below).
iv. “No load ICE operation modes” are defined as ICE operation modes, where the internal combustion engine is stopped.
The above mentioned idle engine operation mode (see item iii) describes all ICE operation modes where the engine is running at idle speed. Idle speed is the rotational speed which the ICE runs on when the engine is decoupled from the drivetrain and the accelerator of the ICE is released. Usually, the rotational speed is measured in revolutions per minute (rpm) of the crankshaft of the ICE. At idle speed the ICE generates enough power to run reasonably smoothly and to operate accessory equipment (water pump alternator and other accessories such as a power steering), but usually not enough energy to perform substantial work such as propelling the vehicle. For vehicles, such as trucks or passenger cars, idle speed is customarily between 600 rpm and 1000 rpm. Even if the accelerator is released a certain amount of fuel is injected into the ICE in order to keep the ICE running. If the ICE is operating a large number of accessories or accessories requiring a lot of energy, particularly air conditioning, the idle speed is normally raised to ensure that the ICE generates enough power. Therefore, most engines have an automatic adjustment feature in the carburetor of the fuel injection system that raises the idle speed when more power is required.
The above mentioned motoring engine operation mode (item iii) is defined as the mode where the ICE is running above a certain rotational speed (rpm), but no fuel is injected into the ICE. One example of a motoring ICE operation mode is when the ICE is dragging, i.e. the vehicle which is normally driven by the ICE is coasting down a hill. During this mode the accelerator is also released, but the engine remains coupled to the drivetrain and the ICE is kept running by the drive fuse of the gearbox's main shaft.
In a vehicle comprising an exhaust gas arrangement based on a Rankin cycle, the different ICE operation modes constitute a problem since the energy generation and the energy distribution of the exhaust gas arrangement cannot be controlled. For an expander engine converting energy to the crankshaft of a vehicle this means e.g. there can be a large time lag before the expander engine gives full power when power is needed. It can also mean that the provision of additional propulsion energy may be unwanted in low load ICE operation modes, particularly when the vehicle is running downhill. If the exhaust gas arrangement acts as auxiliary power unit, such that it generates power to e.g. a battery, a lower efficiency may result, with the addition of cost for the generator, battery and other related pieces of equipment. It has therefore been suggested to control the volume of steam entering the expander engine by providing a bypass for the expander engine.
A further known problem during low load ICE operation modes is that the temperature of the exhaust gas of the ICE decreases significantly as the ICE more or less pumps fresh air at ambient temperature into the exhaust gas system. A heat exchanger arranged in the exhaust gas system for operating an exhaust gas arrangement decreases the exhaust gas temperature even further. This results in at least two disadvantages:
i. The temperature of the exhaust gas is not sufficient for vaporizing the working fluid, thereby rendering the exhaust gas arrangement inoperable.
ii. An optionally provided exhaust gas treatment system, which usually requires a working temperature between roughly 250° C. and 450° C., is cooled below its working temperature.
Consequently, after a long period of low load ICE operation mode, e.g. after a long downhill course, neither the exhaust gas arrangement, nor the exhaust gas treatment system are working properly.
In EP 2 098 696 A1 a second heat exchanger is arranged in the exhaust gas system upstream of the first heat exchanger which is located downstream of an exhaust gas treatment system. The second heat exchanger is located upstream of an SCR catalyst within the exhaust gas treatment system in order to lower the exhaust gas temperature to protect the SCR catalyst from superheating.
It is desirable to provide an exhaust gas arrangement which acts as auxiliary power unit for an internal combustion engine but which alleviates or at least reduces the above mentioned disadvantages of the prior art.
The present disclosure provides according to a first aspect an exhaust gas arrangement comprising an exhaust gas system for conveying an exhaust gas stream, wherein the exhaust gas system comprises a turbine and an exhaust gas treatment system. The exhaust gas arrangement further comprises a working fluid circulation circuit connected to the exhaust gas system for exchange of energy between the exhaust gas stream and a working fluid within the working fluid circulation circuit. The working fluid circulation circuit comprises a first heat exchanger which is arranged at a waste heat source for exchange of energy between the waste heat source and the working fluid, and a second heat exchanger positioned in the exhaust gas system for exchange of energy between the exhaust gas stream and the working fluid. The second heat exchanger is positioned downstream of the turbine and upstream of a particle filter in the exhaust gas treatment system.
Positioning of a second heat exchanger downstream of the turbine and upstream of the particle filter in the exhaust gas treatment system may be used for keeping particle filter in the exhaust gas treatment system within its favoured operating temperature range. This enables that the exhaust gas stream out of the exhaust gas treatment system may be used for not only cooling the exhaust gas stream before entering the particle filter, but also for heating the exhaust gas stream upstream of the particle filter. The particle filter may consequently not only be protected from superheating, but also from being too cold such that regeneration thereof is limited or even made impossible. When the second heat exchanger is used for cooling the exhaust gas stream it is made to further heat the working fluid which first has passed through the first heat exchanger where it may recover energy from the waste heat source. The working fluid may this way even become superheated and used for additional power recovery. When the second heat exchanger is used for heating the exhaust gas stream it is made to cool the working fluid which first has passed through the first heat exchanger where it may recover energy from the waste heat source. In this case any regeneration of the particle filter can be achieved quicker. The second heat exchanger may consequently be used both for heating and for cooling of the exhaust gas stream, such that optimal, or nearly optimal operating conditions may be established for the particle filter and possibly any other features located downstream of the second heat exchanger.
According to an embodiment the second heat exchanger is positioned upstream of any part of the exhaust gas treatment system. Hereby the temperature of the passing exhaust gas stream may be adapted to any part of the exhaust gas treatment system for better performance.
According to an embodiment the waste heat source is any external or internal waste heat source. An external heat source of the exhaust gas arrangement may e.g. be an internal combustion engine to which the exhaust gas arrangement is connected, or an exhaust gas recirculation conduit in the internal combustion engine.
According to an embodiment the internal waste heat source may e.g. be exhaust gas treatment system. The exhaust gas stream may contain more energy in the form of heat than has been recovered in the second heat exchanger and this energy may be used as source for the heat exchange in the first heat exchanger.
According to an embodiment the second heat exchanger is positioned upstream of the first heat exchanger. Hereby the second heat exchanger meets the exhaust gas stream first.
According to an embodiment the first heat exchanger is positioned downstream of an SCR catalyst in the exhaust gas treatment system. The temperature of the SCR catalyst is hence not affected by the heat exchange within the first heat exchanger which may be mainly aimed for recovering heat from the exhaust gas stream such that the exhaust gas stream downstream thereof is cooled down.
According to an embodiment the first heat exchanger is positioned downstream of any part of the exhaust gas treatment system. Parts of the exhaust gas treatment system may be negatively affected if the first heat exchanger is positioned upstream thereof, since their efficiency may depend on a particular temperature interval. Hence it is advantageous to position the first heat exchanger downstream of any part of the exhaust gas treatment system.
According to an embodiment the working fluid circulation circuit comprises an expander engine arranged downstream of the first heat exchanger. One exemplary embodiment of an expander engine is a turbine. An expander engine may be used to recover energy from the working fluid.
According to an embodiment a bypass passage is arranged in the working fluid circulation circuit for bypassing the expander engine, the bypass passage being branched off downstream of the first heat exchanger and is being reconnected to the working fluid circulation circuit downstream of the expander engine. This way expansion of the working fluid and consequently no addition of energy to the expander engine will take place. There may be periods when such addition of energy to the expander engine, and possibly to any other parts to which the exhaust gas arrangement is coupled, such as an internal combustion engine, is contra productive. Such periods may be the earlier defined low load ICE operation modes.
According to an embodiment the bypass passage is branched off upstream of the second heat exchanger. The bypass passage together with the second heat exchanger has a plurality of advantages, e.g.:
i. During low load ICE operation modes, the bypass passage enables the working fluid to bypass the expander engine so that the expander engine is not operated and no additional power is provided to i.e. a drivetrain.
ii. During low load ICE operation modes, the heat of the working fluid may be exchanged to the exhaust gas stream by means of the second heat exchanger in combination with the bypass passage so that the particle filter and an optionally provided exhaust gas treatment system may be kept within its working temperature range by the heated exhaust gas stream.
iii. During high load ICE engine operation modes in turn, the second heat exchanger may be used for superheating the working fluid, whereby the energy exploit of the exhaust gas arrangement may be increased.
According to an embodiment the working fluid circulation circuit further comprises a condensation device arranged downstream of the expander engine for condensing the working fluid, and a first pump for circulating the working fluid. Advantageously, the exhaust gas arrangement is based on a Rankin cycle. Thus, the exhaust gas arrangement may further comprise a condensation device for cooling and thus converting the gaseous working fluid into its liquid phase, and a first pump for circulating the working fluid.
According to an embodiment the first pump is arranged downstream of the condensation device. Pumping a liquid to high pressure is easier relatively seen than compressing a gas to similar pressure. Also, when the liquid is cooled to well below boiling temperatures the pump may be of relative simple design.
According to an embodiment the bypass passage is reconnected to the working fluid circulation circuit either upstream or downstream of the condensation device.
When the bypass passage is reconnected to the working fluid circulation circuit upstream of the condensation device and since the working fluid streaming through the bypass passage may be at least partly in its gaseous phase, the condensation device ensures that also the gaseous phase part of the bypassed working fluid is condensed into its liquid phase so that the pump is not destroyed by cavitation. The bypass passage may also be reconnected to the working fluid circulation circuit downstream of the condensation device such that, particularly, it is ensured that the working fluid in the bypass passage is in its liquid phase.
According to an embodiment when the bypass passage is reconnected to the working fluid circulation circuit downstream of the condensation device the bypass passage is reconnected to the working fluid circulation circuit downstream of the first pump. This way the first pump does not need to be dimensioned for the higher flow which is the result from utilising a liquid for heat transport in the heat exchange in the exhaust gas arrangement.
According to an embodiment a second pump is arranged in the bypass passage downstream of the second heat exchanger. This way the first pump does not need to be dimensioned for the higher flow which is the result from utilising a liquid for heat transport in the heat exchange in the exhaust gas arrangement. The pumping effect may instead be accomplished by the second pump.
According to an embodiment a first valve is arranged in the working fluid circulation circuit downstream of the branch off of by the bypass passage and upstream of the expander engine for opening and/or closing the connection to the expander engine, and/or a second valve is arranged in the bypass passage for opening and/or closing the bypass passage.
According to an embodiment the bypass passage is split into at least a first branch and a second branch, wherein the first branch is arranged to reconnect the working fluid circulation circuit downstream of the expander engine, and the second branch is adapted to reconnect the working fluid circulation circuit upstream of the expander engine. There may be several reasons and advantages for doing so. During heavy engine braking the exhaust gases will become hot and there may be a lot of gas phase working fluid which is preferably not run through the expander engine. It may also be advantageous to bypass the exhaust gas after treatment system for regeneration of parts thereof. Furthermore, there are different expander engine types and these can endure different amounts of liquid droplets. When the expander engine demands superheated steam for proper function and to guarantee a working fluid free from liquid, the working fluid should preferably be superheated in the first heat exchanger and to some extent be made to bypass the second heat exchanger to separate some condensate downstream of the second heat exchanger to mix superheated steam with steam upstream of the expander engine.
According to an embodiment the second valve is arranged in the first branch for opening and/or closing the first branch, and a third valve is arranged in the second branch for opening and/or closing the second branch.
According to an embodiment the first and/or the second and/or the third valve is/are an on/off valve. An on/off valve is easily controlled and robust.
According to an embodiment the first valve is a normally open valve and/or the second and/or third valve is/are a normally closed valve. This ensures that even if one or several of the valves are inoperable, e.g. due to a broken valve controller, the expander engine and thereby the exhaust gas arrangement may still be operated.
According to an embodiment the bypass passage further comprises a separator arranged downstream of the second heat exchanger for separating the working fluid streaming through the bypass passage into a first stream of preferably liquid working fluid and a second stream of preferably gaseous working fluid. The first branch may reconnect the working fluid circulation circuit downstream of the expander engine, and the second branch may reconnect the working fluid circulation circuit upstream of the expander engine. As mentioned above, the second heat exchanger may also be used for superheating the working fluid, particularly during high load ICE operation modes. For the advantageously increased exploit of thermal energy, the superheated working fluid needs to be fed to the expander engine, which is done by the arrangement of the second branch.
According to an embodiment the separator is arranged at the location where the bypass passage branches into the first and second branch, so that the first stream of working fluid is guided through the first branch and the second stream of working fluid is guided through the second branch. It is thereby ensured that the gaseous working fluid drives the expander engine, wherein the liquid working fluid may stream to the cool side of the exhaust gas arrangement. In this arrangement, the bypass passage, or more precisely, the first branch of the bypass passage may also be reconnected downstream of the condensation device. Since only liquid working fluid streams through the first branch to the pump, cavitation may be avoided. It goes without saying that the first branch of the bypass passage may be reconnected downstream of the pump and may comprise its own second pump.
According to an embodiment the expander engine is adapted to be drivingly connected to a drivetrain of a vehicle for providing auxiliary power thereto in order to lower any fuel consumption of the vehicle. An exemplary embodiment of such connection between the expander engine and the drivetrain is through a gear set.
According to an embodiment the expander engine is adapted to be drivingly connected to a generator of a vehicle in order to provide electric power to accessories of the vehicle. Such accessories may e.g. be an electric motor for hybrid operation of the vehicle, other power using devices in or around the vehicle.
According to an embodiment the arrangement further comprises a thermoelectric element for generating electric energy for driving a consumer, wherein the thermoelectric element comprises a thermoelectric material having a first side and a second side, wherein for generating electric energy, the temperature of the first side is adapted to differ from the temperature of second side, and/or wherein by supplying electric energy to the thermoelectric element, the temperature of the first side differs from the temperature of the second side. The first side vision heatable and the second side is kept at a lower temperature, e.g. is cooled by a cooler, the condensation device and/or simply by the cool working fluid of the working fluid circuit. The induced temperature difference between the first and second side may then generate, in the known way, an electric current in the thermoelectric material which can be used e.g. for driving an accessory equipment.
Thereby, the generation of electric energy is based on the so-called Seebeck effect which governs the conversion of a temperature difference directly into electric energy according to the formula:V=∫nn(SB(T)−SA(T))dT, 
wherein V is the voltage, SA and SB are the so-called Seebeck coefficients of material A and material B, and T-i is the temperature of the material on the first side and T2 the temperature of the material on the second side.
Besides the generation of electric energy it is also possible to supply electric energy to the thermoelectric element. Then, the thermoelectric element functions as heater on its one side and cooler on its other side. This effect is the so-called Peltier effect stating: When a current is made to flow through a thermoelectric material composed of materials A and B, heat is generated at one side T2, and absorbed at the other side at T∧ The Peltier heat absorbed by the other side per unit time is equal to{dot over (Q)}=ΠABI=(ΠB−ΠA)I, 
where ΠAB is the Peltier coefficient for the thermoelectric material composed of materials A and B and ΠA(ΠB) is the Peltier coefficient of material A (B). Π varies with the material's temperature and its specific composition:
The principle of an exhaust gas arrangement using a thermoelectric material is outlined e.g. in WO 2011/011795.
Consequently, the provision of a thermoelectric material in the exhaust gas arrangement has several advantages:
i. The expander engine provides mechanical work to the drivetrain while the thermoelectric material provides electric energy to accessories.
ii. Provision of the thermoelectric material in the condensation device of a Rankin cycle may utilize waste heat from the Rankin cycle.
iii. Provision of the thermoelectric material in at least one heat exchanger increases the total heat recovery, since the working fluid is heated by the waste heat of the thermodynamic material.
iv. When an external electric power source is connected to the thermoelectric material the thermoelectric material may be used as heater and/or cooler for the working fluid resp. the exhaust gas stream.
According to an embodiment the first side is arranged in heat exchanging connection to the waste heat source.
According to an embodiment the second side is arranged in heat exchanging connection to the working fluid circulation circuit.
According to an embodiment the thermoelectric material is arranged in at least one of the heat exchangers, e.g. in the first and/or second heat exchanger.
According to an embodiment the thermoelectric material is arranged in the condensation device.
According to an embodiment the thermoelectric element is adapted to be powered by an external electric energy source. Additionally, the thermoelectric material may be adapted to be powered by a battery or by an alternator during a cold start of the engine. Thereby, the thermoelectric material may be used as heater, which transfers heat from the working fluid to the exhaust gas stream and further on to the exhaust gas treatment system. Consequently, the exhaust gas treatment system may be heated up quickly to a working temperature for an efficient emission reduction.
Additionally or alternatively, the thermoelectric material may be powered by a battery or directly from an alternator during a cold start of the engine in such way that heat is transferred from the exhaust gas stream to the working fluid. Thereby, extra power may be provided to the drivetrain of the vehicle, even if all heat from the exhaust gas is already used for heating the exhaust gas treatment system.
As soon as the exhaust gas treatment system has reached its desired working temperature, the thermoelectric material may be switched from the heater mode to the generator mode by terminating the electric power supply. Then, the thermoelectric material itself produces electric energy for driving accessories by converting heat from the exhaust gas into electric energy.
According to a further embodiment the thermoelectric material may be powered by the battery or the alternator when the internal combustion engine is in low or no load ICE operation mode. Thereby the exhaust gas stream may be heated in order to avoid cooling down of the exhaust gas treatment system. Advantageously, in case the thermoelectric material is powered by the alternator of the internal combustion engine, e.g. during a downhill drive, the powering of the thermoelectric material may act as an auxiliary brake for the vehicle.
According to a second aspect of the disclosure an internal combustion engine system is disclosed, comprising an internal combustion engine and an exhaust gas arrangement of a kind according to any one or a combination of the embodiments of the first aspect of the disclosure.
According to a third aspect of the disclosure a vehicle is disclosed, comprising an exhaust gas arrangement of a kind according to any one or a combination of the embodiments of the first aspect of the disclosure, or an internal combustion engine system of a kind according to any one or a combination of the embodiments of the second aspect of the disclosure.
Further advantages and embodiments are defined in the description, the figures and the appended claims.